In the maize seed the prolamine zein comprises 50% of the stored protein. The protein bodies containing the zein have polysomes associated with their limiting membrane. We have shown that only the two polypeptides which make up zein are synthesized at the surface of these organelles. A number of proteins are known to be made on membrane-bound polysomes and then transported across the membrane in other eukaryotes. The zein synthetic apparatus is unique because large quantities of the machinery devoted to the synthesis and processing of a single protein can be easily isolated. A number of nonallelic mutations exist which specifically interrupt zein synthesis without affecting the nature of the protein itself. These mutations may be useful in studying this phenomenon because they are likely to be lesions for certain of the components specifying that a single message is translated on a particular membrane and that its product is transported across that membrane. Since zein polysomes can be separated from all others by first isolating protein bodies, we have a relatively easy method of preparing the zein messenger RNA. We anticipate that this will be the first homogeneous message prepared from a higher plant. In addition to learning some of its characteristics, it will allow us to investigate gene dosage and the rate of message formation. Because zein is the major protein in the corn kernel and lacks lysine and tryptophan, the two essential amino acids limiting in cereals, it is directly related to the problem of nutritional quality of normal size. Mutants which depress zein synthesis, as in the case of the "high lysine" mutant, opaque-2, produce kernels with a better overall amino acid composition. Because there are secondary problems associated with these mutants, it may be desirable instead to attempt to alter kernel amino acid composition by mutationally affecting the amino acid composition of zein. To accomplish this, we need to find variants of the zein polypeptides and use them to map the zein structural genes.